Current Traffic Collision Avoidance System (TCAS) installations are expensive. Dual TCAS installations are even more so because they require an extensive amount of cable and/or coaxial cable switches. U.S. Pat. No. 4,855,748 describes a system and method for determining TCAS bearing estimation using a four-element planar array antenna. TCAS installations typically use two such four-element antennas, one on the top surface of an aircraft, and the other on the bottom surface of the aircraft. This typically requires a coaxial cable connection for each antenna element, resulting in at least eight total cables. This results in considerable weight and expense.
Commonly owned U.S. Pat. No. 7,583,223, which is hereby incorporated by reference as if fully set forth herein, discloses a system that includes a first antenna and a second antenna located on a top surface of an aircraft, spaced apart along a first axis, as well as a third antenna and a fourth antenna located on a bottom surface of the aircraft, spaced apart along a second axis orthogonal to the first axis. The system also includes a transmitting, receiving, and processing system coupled to the first, second, third, and fourth antennas, wherein the transmitting, receiving, and processing system is configured to transmit TCAS interrogations, receive TCAS replies, and process the TCAS replies to determine the relative bearing of a second aircraft from the first aircraft. Such a system provides a TCAS antenna system, employing two pairs of two-element arrays, that uses less cabling than previous attempts, specifically, four cables (two to top and two to bottom) instead of eight cables (four to top and four to bottom).
Commonly owned U.S. Pat. No. 4,855,748 discloses an approach by which cables associated with four-element antenna arrays may be phase calibrated. However, such approach cannot be employed for phase calibration of the above-described two-element arrays.